1. Field of the Invention
This invention relates to a novel process for the acetylation of a mono-substituted phenol and a mono-substituted naphthol which comprises reacting respectively a mono-substituted phenol and a mono-substituted naphthol with an acetylating agent vinyl acetate at a low temperature. The substituent in the mono-substituted phenol referred to above is selected from the group consisting of halo, hydroxy and carboxy at o-, m-, or p-position with respect to the hydroxy group of the phenol, while the mono-substituted naphthol referred to above is 2-hydroxy-6-naphthoic acid.
The acetylated final product, for example, p-acetoxybenzoic acid finds its use as a monomer in the production of liquid-crystal polymers such as "Vectra" and "X7G", etc. Such polymers provide high heat resistance, tensile strength and dimensional stability, which improve the qualities of Engineering Plastics among different fields.
2. Brief Description of the Prior Art
Traditionally p-acetoxybenzoic acid is prepared by acetylation with more expensive acetic anhydride, under more drastic reaction condition. References relating to the preparation and application of p-acetoxybenzoic acid copolymers are cited in following literature:
U.S. Pat. Nos. 4,083,839; 4,161,470; 4,219,461; 4,264,802; 4,267,289; 4,279,803; 4,299,756; 4,318,841; 4,355,132; 4,355,133; 4,355,134; 4,429,100; 4,473,682; 4,522,974 Other acetylated final product, such as phenyl acetate finds its use as an organic solvent or intermediate for various organic syntheses. The advantages of using vinyl acetate instead of the traditional acetic acid, acetic anhydride or acetyl chloride as the acetylating agent are as follows:
(1) the reaction is carried out at a temperature lower than 100.degree. C.;
(2) the reaction by-product can be easily separated under the reaction condition; and
(3) due to a lower reaction temperature and a less acidic environment a less expensive construction material may be used for the reaction system.
Acetylation of phenolic compounds and naphtholic compounds is usually more difficult than that of aliphatic compounds because of more the acidic nature of the phenolic hydroxy group and the naphtholic hydroxyl group. As a result, the reaction usually requires a higher temperature and a stronger acidic condition, and the product isolation is more difficult due to a more complicated reaction mixture. Therefore, a higher cost of production is usually required.
Acetic anhydride and acetyl chloride are two common acetylating agents used in the industry. Both are sensitive to hydrolysis, and water has to be carefully removed during the course of the reaction. During the reaction the former yields one equivalent of acetic acid, and the latter gives one equivalent of hydrogen chloride. Recovery of acetic acid needs an expensive distillation step. Hydrogen chloride may cause severe corrosion problems for the production equipment and may result in an extra load for waste water treatment.